The present invention relates to an absorbent structure consisting of an absorbent material layer and a high-loft material layer, and to a method for producing an absorbent structure which is intended for use in an absorbent article, such as a sanitary towel, panty liner, incontinence pad, diaper, bandage, saliva absorber, or the like.
Absorbent articles of this type are known in a large number of designs. The absorption body in these products can be produced by means of cellulose pulp, for example in rolls, bales or sheets, being dry-defibered and converted in fluffed form to a pulp to a pulp mat, sometimes with admixture of so-called superabsorbents, which are polymers having the ability to absorb several times their own weight of water or bodily fluid.
The pulp body is often compressed, on the one hand in order to increase its ability to spread liquid, and on the other hand to reduce the bulk of the pulp body and obtain a product which is as compact as possible.
It is of great importance for these products that they have a high absorption capacity, that the total absorption capacity is fully utilized, and that the materials included have a good ability to spread the absorbed liquid. The product should also be thin so that it can be used as discreetly as possible.
SE,B,462 622 describes a readily disintegratable product comprising cellulose-containing fibre material, which product is of such a strength that it can be rolled up or handled in sheet form for storage and transportation, without addition of chemicals which increase the bonding strength between the fibres. Flash-dried fibres of a chemithermomechanical pulp, so-called CTMP, with a dry matter content of about 80%, are formed into a web. The fibres are conveyed by an air stream, in a controlled flow, through a forming head arranged over a wire. The air is sucked off through a suction box arranged under the wire. The web is pre-pressed in order to reduce the web bulk prior to the final pressing to a density of 550-1000 kg/m.sup.3. This product is easy to dry-defibre and to convert to fluffed form for production of, for example, hygiene articles such as diapers, sanitary towels and similar products. The advantage of the material is that the cellulose pulp in roll form is flash-dried and dry-formed into a web, and the pulp thus has a low content of paper bondings, for which reason the defibering energy is lower than for conventional wet-formed pulp. This also affords possibilities of compressing the material hard, inter alia for reducing the transportation and storage volumes, etc., while retaining the low defibering energy. Another advantage is that superabsorbents can be mixed into the dry-formed material, something which is not possible as regards wet-formed material.
It has been found that this dry-formed material in the non-defibered state is a very good absorption material, and it is possible for the material to be used directly, without defibering, as an absorption material in hygiene articles. This is disclosed in the applications SE 9203445-3 and SE 9203446-1. The material also has good spreading properties and swelling properties. A simpler and less costly production process is achieved, and the conventional defibering and the conventional mat formation are not required. For certain product applications in hygiene articles, it is expedient for dry-formed roll pulp to undergo softening prior to use as absorption material. The good absorption properties and swelling properties already mentioned are not affected to any great extent by the softened process.
An absorbent structure often has an admission layer/transport layer on top of an absorbent material layer. The admission layer/transport layer can be a high-loft material (see EDANA definition) which is produced by, for example, through-air bonding (see definition of through-air thermal bonding in EDANA) and consists of synthetic fibres such as polyester, polypropylene or mixtures thereof. A mat of fibres is carded out to form an open layer and is allowed to pass through an oven. The fibres have different melt points and the heat therefore affects the different fibres in account of the fact that some of the fibres melt. Those fibres which do not melt retain an open and aired structure.
When an admission layer/transport layer in the form of a high-loft material or the like is to be bound to an absorption material layer, this must be done in such a way that, on the one hand, the high-loft material fixes in the absorption material layer, and, on the other hand, the transfer of liquid from the high-loft material to the absorption material is not impeded. The normal procedure is quite simply to lay a high-loft material layer directly on the absorbent material layer.
One problem is that the contact between the two layers may become poor. The transfer of liquid from the high-loft material to the absorption material then deteriorates, which is a serious disadvantage for this type of product. It is also conceivable to glue the high-loft material on, but glue impairs the transfer of liquid.
Another problem is that the poor contact between the layers results in the product being of poor strength. The layers can detach from each other and the absorption material can be delaminated.
The object of the invention is to solve these problems.